Re: LED at 60 HZ? (was RE: Radio Shack Strobes)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Yipps!!

Before all you point out the errors of my ways...  That little devil on me 
shoulder pointed out that "Terry, you screwed all up there... 
"persistence!!""  Although the rise time may be very fast, the fall time is 
where the problem may be...  And so it does:

http://hot-streamer-dot-com/temp/WhiteLED-3.gif

Yeah!!  66mS!!

If science were easy, everyone would do it...

Cheers,

         Terry




>Hi,
>
>White LEDs bombard phosphors with UV light to make the bright white 
>light.  Just like a CRT or common florescent tube.  They probably flash 
>well at 60Hz but they may indeed be poor for a strobe that need to turn on 
>and off in significantly less than 1mS.  I wonder what the frequency 
>response of white LEDs is?  but don't want to drag it OT...  I note that 
>the new electronic ballast florescent lights that operate from 50 to 
>100kHz can destroy IR communications, so the brighter phosphores may be 
>very fast...
>
>Since I got the stuff to test it...  I just flashed my 1GHz fiber probe 
>input with one of those key-chain style white LEDs.
>
>http://hot-streamer-dot-com/temp/WhiteLED-1.jpg
>
>and the answer is...
>
>http://hot-streamer-dot-com/temp/WhiteLED-2.gif
>
>literally, as quick as lighting at 165nS ;-))  So the frequency response 
>of white LEDs is probably a few orders of magnitude faster than any strobe 
>light needs :-)))
>
>
>Cheers,
>
>         Terry
>
>
>At 05:16 PM 2/24/2004, you wrote:
>>On 24 Feb 2004, at 13:10, Tesla list wrote:
>>
>> > Original poster: "Daniel Kline" <daniel_kline-at-med.unc.edu>
>> >
>> > An engineering friend says a high-brightness LED on a
>> > low-voltage transformer, like 6 Volts, connected through
>> > a suitable resistance, should flash at 60Hz in sync with
>> > the 60Hz mains. (50Hz for you all over there :)
>> > It seems too easy to me...he thinks that the LED may have
>> > a "persistence" issue. In other words, just because it
>> > turns off quickly doesn't mean it stops emitting quickly.
>> > Comments?
>>
>>The persistence can't be great considering LEDs are used to convert
>>electrical impulses to light impulses at GHz frequencies. Any
>>perceived persistence is probably a function of propagation time from
>>eyes to brain or some other physiological thing to do with the eyes.
>>
>>Malcolm